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White-Dwarf Planets

StarDate:

October 16, 2012

Astronomers have found planets orbiting all kinds of stars. Yet they haven’t found planets orbiting the dead stars known as white dwarfs. But one astronomer says they shouldn’t be hard to find — and that some of those planets could even be like Earth.

A white dwarf is the dead core of a once-normal star like the Sun. It no longer produces nuclear energy, but it continues to shine because it’s extremely hot. The typical white dwarf is about 60 percent as massive as the Sun, but only about as big as Earth.

White dwarfs are so dim that not a single one is visible to the unaided eye. Yet they’re quite common — they account for one of every 20 stars in the Milky Way galaxy.

Last year, Eric Agol of the University of Washington wrote that white dwarfs could harbor Earth-like planets at just the right distance from their star for life to exist.

Agol reported that if such planets exist, they should be easy to find. Because a white dwarf is so small, an Earth-sized planet that passed in front of it would block nearly all of the star’s light. Detecting such a deep eclipse would require only a small, inexpensive telescope.

The idea is highly speculative, though, because it doesn’t explain how a planet would survive the process that created the white dwarf in the first place. Even so, it gives astronomers one more place to look for planets — including worlds that could be similar to our own.

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